1. Field of the Invention
This invention relates to a device for providing signature stacks with endboards and for conveying said stacks in stackers for printing works and the like.
2. Description of Related Art
Signature-stacking, as performed in printing works and the like by means of conventional stackers, normally require that special boards be placed at the respective ends of the stacks once they are completed, the function of such boards being that of preventing the signatures placed at the ends of said stacks from suffering damage as may be caused by pressing rams and binding straps when tamping, or pressing, and binding said stacks. Such damage, in fact, normally results from the exceedingly high pressure exerted on the stacks--in the region of e.g. 600 kgs--during binding.
Such boards are generally placed manually by an operator. While the incoming signatures are carried by the swing plate, the fork of the lift truck is raised to its uppermost position; hence a first board is placed by the operator, which thus becomes the bottom endboard. Then the swing plate is lowered and the formed part of the stack is placed onto said endboard, after which the plate is retracted and raised while more signatures are loaded on to the fork. The process is carried on until the desired stack height is achieved, at which point the operator places a second endboard at the top of the stack, namely, the top endboard. Hence the fork places the full stack onto the roller unit defining the bottom of the stack-forming shaft, which is designed to convey the stack toward the binding station. As the stack is placed on the bottom of the stacker, another manual operation must be performed, in that the operator must see to the effective conveyance of the stack from said stack-forming shaft to the binding station. The stack is supported by the roller bottom and rests against the stacker roller board. Conveyance is effected as follows: the operator places one hand onto the top endboard and with his other hand exerts pressure on the stack in order to drive it along the conveyance track. As the stack reaches the binding station, two rollers are lifted out of the roller board and pressed against the sides of the stack so as to keep it in the required position during pressing of same. These rollers, therefore, act as mobile side members. Pressing is normally effected by means of two adjacent vertical cylinder-ram units, whereas binding is carried out by means of a conventional skein-winder, employing e.g. thermoplastic straps.
Where conventional stackers are employed, an operator is needed also in order to prevent the stack from hollowing out on one side and bulging on the other when the stack itself is being lowered (this defect is commonly referred to as a "banana-shaped stack" and is particularly likely to occur where the signatures are folded in-and-in); for otherwise the stack would most probably collapse as soon as it is left loose or placed onto the conveyor. In order to prevent this from happening, the operator places one hand onto the top end of the stack and uses his free hand to correct any misalignment. Where conventional stackers are used, therefore, the operator must perform three functions, namely:
1. place the boards at the ends of the stacks;
2. check, and if necessary see, that the stacks are kept in the upright position after loading them onto the roller bottom of the stacker; and
3. push to stacks along the conveyance path leading from the stack-forming shaft to the binding station.
The applicant has already submitted two designs (Italian Patent Application Ser. Nos. 20344 A/83 and 20345 A/83) relating to an automatic endboard-feeding device for endboards produced in just one size; these designs, however, require the use of two loaders and imply a considerable amount of circuitry. In addition, these loaders are designed to operate with endboards of a definite size, hence are unable to meet the varying operating requirements dictated by signatures of different sizes. These designs feature, furthermore, a stack-conveying device, which in turn implies considerable construction costs, besides depending for its operation on a definite signature size.